Use of pegylated photosensitizer conjugated with an antibody for treating abnormal tissue

ABSTRACT

A photosensitizer suitable for use in administering photodynamic therapy (PDT), conjugated with antibodies that are targeted to antigens on abnormal tissue and polyethylene glycol (PEG) or other polymer that extends the residence time of the conjugate within a patient&#39;s body. The resulting pegylated targeted conjugate is administered to a patient, and after the antibodies have had sufficient time to bind with the antigens, light from an external or internal source having a waveband corresponding to an absorption waveband of the photosensitizer is administered. Use of an external light source that emits relatively long wavelength light enables the light to pass through any intervening dermal layer and normal tissue between the external light source and the treatment site. Since the photosensitizer in the conjugate is bound to the abnormal tissue, the light therapy has minimal effect on the intervening normal tissue. Furthermore, the efficacy of the PDT is enhanced due to the increased concentration of the photosensitizer of the conjugate linked to the abnormal tissue.

FIELD OF THE INVENTION

[0001] The present invention is generally related to the use of lighttherapy to destroy abnormal tissue that has absorbed a photosensitizer,and more specifically, to the use of a photosensitizer that is targetedto bind with the abnormal tissue, but not normal tissue, so that thelight administered during the therapy has a minimal adverse effect onsurrounding normal tissue, which is generally free of thephotosensitizer.

BACKGROUND OF THE INVENTION

[0002] Abnormal tissue in the body is known to selectively absorbcertain photosensitizer dyes that have been administered to a patient toa much greater extent than normal tissue surrounding a treatment site.For example, tumors of the pancreas and colon may absorb two to threetimes the volume of these dyes, compared to normal tissue. The cancerousor abnormal tissue that has absorbed the photosensitizer dye can then bedestroyed by administering light of an appropriate wavelength orwaveband corresponding to an absorbing wavelength or waveband of thephotosensitizer dye. This procedure, which is known as photodynamictherapy (PDT), has been clinically used to treat metastatic breastcancer, bladder cancer, lung carcinomas, esophageal cancer, basal cellcarcinoma, malignant melanoma, ocular tumors, head and neck cancers, andother types of malignant tumors. Because PDT may selectively destroyabnormal tissue that has absorbed more of the dye than normal tissue, itcan successfully be used to kill the malignant tissue of a tumor withless effect on surrounding benign tissue than alternative treatmentprocedures, such as traditional chemotherapy or radiation therapy.

[0003] However, even those photosensitizers that are much moreselectively absorbed by abnormal tissue will still be absorbed to somelesser extent by the normal tissue of a patient's body. If the lighttherapy administered is limited primarily to the abnormal tissue at thetreatment site so that very little light is applied to the adjacentnormal tissue, which has absorbed the photosensitizer to a lesserextent, the effect of the light therapy on such normal tissue will beminimal. To enable the selective application of light therapy to aninternal treatment site with minimal exposure of surrounding normaltissue, it is typically necessary to either surgically expose theinternal treatment site, or insert an appropriate light source probeinto the patient's body and advance it to the treatment site, forexample, using conventional endoscopic procedures, or insert a lightsource probe interstitially into a tumor.

[0004] More recently, techniques have been developed for administeringlight therapy to an internal treatment site from an externally disposedlight source. These techniques take advantage of the fact that lighthaving a relatively long wavelength will readily penetrate dermal tissueto activate photosensitizers absorbed by abnormal tissue at an internaltreatment site. The disadvantage of this approach is that normal tissuelying between the light source and the internal treatment site is alsois irradiated by the light as it passes through the overlying tissue tothe internal treatment site. Skin and other normal tissue in thepropagation path of the light administered externally to render PDT toan internal treatment site will thus be adversely affected by thetherapy. The effects of the light therapy on normal tissue that hasabsorbed the photosensitizer may range from mild reddening of the skinto severe damage to the normal dermal tissue. Clearly, it would bedesirable to minimize damage to the normal tissue by substantiallyreducing the extent to which the normal skin and tissue absorb thephotosensitizer.

[0005] One approach developed to address the preceding problems is tobind antibodies to a photosensitizer that are targeted to the abnormalcells at a treatment site. When a photosensitizer conjugated with anantibody is administered to a patient, the antibodies will tend to bindthe photosensitizer to the abnormal tissue, but not to normal tissue,thereby improving the specificity of the PDT and avoiding harm to thenormal tissue. However, it has been shown that targeted photosensitizersthat are conjugated with an antibody can have a relatively low uptake byabnormal tissue in a tumor. In some cases, as little as 0.1% of aninjected dose of photosensitizer is actually absorbed by the abnormalcells in a tumor. The low tumor uptake of antibody targetedphotosensitizers (or other drugs) is due in part to the rapid plasmaclearance by the reticuloendothelial system and poor penetration of thetargeted conjugate across vascular endothelium. In effect, the targetedphotosensitizer is cleared too rapidly from the plasma in the patient'sbody to have an opportunity to bind the antibody with the abnormaltissue at the levels desired.

[0006] More generally, too rapid clearance of conventionalphotosensitizers (i.e., a non-targeted photosensitizer) from plasma hasalso been recognized as problem. One solution that has been explored isthe use of a synthetic drug carrier such as polyethylene glycol (PEG).As previously reported by others, PEG coated microparticulatescontaining a photosensitizer (zinc phthalocyanine) have been tested invivo. In addition, V. P. Torchilin has published an article entitled,“Polymer-coated Long-Circulating Microparticulate Pharmaceuticals,” inJournal Microencapsulation, vol. 15, no. 1, (1998) pp. 1-19, in which hediscusses the protective effect of certain polymers, including PEG, onnanoparticulate drug carriers, including micelles, for extending thecirculation time of the encapsulates in solution. PEG is well known as asterically protecting polymer and drug carrier. Useful biologicalproperties of PEG include its water solubility, low immunogenicity, andextended life while circulating in mammalian organisms. A PEG dextranconjugate has been used as a combined stabilizer and surface modifier toproduce resorbable poly(DL-lactide-co-glycolide) (PLG) microparticles byan emulsification/solvent technique as described by A. G. A. Coombes etal. in “Biodegradable Polymeric Microparticles for Drug Delivery andVaccine Formulation: the Surface Attachment of Hydrophilic Species Usingthe Concept of Poly(ethylene glycol) Anchoring Segments,” inBiomaterials 1997, vol. 18, No. 17, page 1153. However, it appears thatprotectively polymerized drugs have not been conjugated with antibodiesthat can target the drugs to abnormal tissue. Clearly, the combinationof a polymer such as PEG to protect a photosensitizer that is conjugatedwith an antibody could solve both the too rapid clearing of conventionaltargeted photosensitizer conjugates from the plasma and ensure that thephotosensitizer binds only to the abnormal tissue, to substantiallyeliminate any damage to the normal tissue by the light therapy. Such acombination has not been disclosed or suggested by the prior art.

SUMMARY OF THE INVENTION

[0007] In accord with the present invention, a method for destroyingabnormal tissue within a patient's body is defined. The method includesthe step of providing a photosensitizer that is characterized byabsorbing light within a defined waveband. The photosensitizer issterically protected by a polymer and is conjugated with an antibodythat is targeted at the abnormal tissue, producing a polymer protectedantibody/photosensitizer conjugate. When the polymer protectedantibody/photosensitizer conjugate is administered to the patient, theantibody portion of the conjugate preferentially links with the abnormaltissue at the treatment site, while the polymer increases an in vivoresidence time of the antibody/photosensitizer conjugate within thepatient's body. Consequently, there is an increased uptake of theantibody/photosensitizer conjugate by the abnormal tissue at thetreatment site. Light within the defined waveband is administered to theinternal treatment site, thereby activating the photosensitizer todestroy the abnormal tissue.

[0008] The polymer in the above-described method is preferablypolyethylene glycol or a derivative of polyethylene glycol and is watersoluble, hydrophilic, and biocompatible. In addition, the polymerexhibits a low toxicity and a low immunogenicity, is not biodegradable,and does not form any toxic metabolites. Other desired characteristicsof the polymer include a high enough molecular weight, combined with ahighly flexible main chain to provide for long in vivo residence timesin a human body. The polymer should have at least one attachment site towhich the photosensitizer and antibody may be covalently bonded.

[0009] The wavelengths of the light used when administering the lighttherapy from an external source are sufficiently long to readily passthrough a dermal layer and through intervening tissue to reach theinternal treatment site. Instead of being administered externally, thelight may be administered internally using a light source disposedinterstitially so that the light is administered to the treatment sitewithin a patient's body.

[0010] The treatment site may be localized, such as at a tumor, or itmay be disseminated throughout at least a portion of the patient's body,and the abnormal tissue may be distributed throughout the treatmentsite. The treatment site may include at least part of a vascular systemof the patient in which the abnormal tissue is disposed. Furthermore,the abnormal tissue may be a tumor, non-localized malignant cells, ormay be a disease causing bacteria or a disease causing virus.

[0011] The method described above may serve as a prophylaxis byadministering the polymer protected antibody/photosensitize conjugateand administering light to a prospective treatment site at whichabnormal tissue may possibly develop. This prophylactic treatment may berepeated at intervals to prevent development of the abnormal tissuewithin the patient.

[0012] It is also contemplated that the method described above may beused following the surgical removal of a substantial portion of theabnormal tissue, to destroy any residual abnormal tissue at thetreatment site, or following the transplanting of bone marrow into apatient, to destroy residual abnormal tissue in the patient's body.

[0013] Another aspect of the present invention is directed to a methodto improve a specificity with which a photosensitizer is taken up byabnormal cells within a patient. In this further aspect of theinvention, a microparticle, a photosensitizer, an antibody that istargeted at antigens on the abnormal cells, and a polymer are provided.The antibody and the photosensitizer are conjugated to themicroparticle, and the microparticle is coated with a polymer thatprolongs an in vivo residence time for the microparticle basedantibody/photosensitizer conjugate. When the polymer coatedmicroparticle based antibody/photosensitizer conjugate is administeredto a patient, the antibody on the conjugate links with the abnormalcells. The linking action of the antibody and ability of the polymercoating to increase the in vivo residence time results in a higheruptake of the polymer coated microparticle basedantibody/photosensitizer conjugate by the abnormal cells than would bepossible using a microparticle based antibody/photosensitizer conjugatethat is not coated with the polymer.

[0014] The microparticle may comprise a micelle. Preferably, the polymeris PEG.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0015] The foregoing aspects and many of the attendant advantages ofthis invention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

[0016]FIG. 1 schematically illustrates a first form of a polymerprotected antibody/photosensitizer conjugate microparticle;

[0017]FIG. 2 is a schematic view showing the polymer protectedantibody/photosensitizer conjugate of FIG. 1 bound to a target malignantcell organelle by the antibody;

[0018]FIG. 3A schematically illustrates a second form of a polymerprotected antibody/photosensitizer conjugate in which a photosensitizingagent and an antibody are bonded to a polymer at separate attachmentsites;

[0019]FIG. 3B schematically illustrates a third form of a polymerprotected antibody/photosensitizer conjugate in which a photosensitizingagent and an antibody are bonded to a polymer at the same attachmentsite;

[0020]FIG. 4 is a schematic view of the third form of a polymerprotected antibody/photosensitizer conjugate bound to a target malignantcell organelle by the antibody;

[0021]FIG. 5 is a schematic cross-sectional view of a portion of apatient's body in which a blood vessel is disposed, showing the polymerprotected antibody/photosensitizer conjugates being injected into thepatient's bloodstream with a syringe;

[0022]FIG. 6 is a schematic cross-sectional view of a portion of apatient's body containing a tumor, showing an external long wavelengthlight source being used to activate the photosensitizers in the polymerprotected antibody/photosensitizer conjugates that are linked to theabnormal tissue in the tumor; and

[0023]FIG. 7 is a schematic cross-sectional view of a portion of apatient's body containing a tumor, showing an internal light sourcebeing used to activate the photosensitizers in the polymer protectedantibody/photosensitizer conjugates that are linked to the abnormaltissue in the tumor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Polymer ProtectedAntibody/Photosensitizer Conjugates

[0024] Referring to FIG. 1, a polymer protected antibody/photosensitizerconjugate 10 a in accordance with the present invention is schematicallyillustrated. Polymer protected antibody/photosensitizer conjugate 10 aincludes a microparticle core 12 of the type normally used as a drugcarrier. It is contemplated that the microparticle may be a micelle or acarrier, such as a latex sphere. Other inert, biocompatiblemicroparticles may be used for the core or carrier. The choice of theparticular microparticle will be determined by a number of factors,including the chemical compatibility of the microparticle with theantibody, the photosensitizer, and the polymer.

[0025] Attached to the surface of microparticle core 12 are a pluralityof antibody linking sites 20, which are specifically targeted to linkwith antigens on abnormal tissue, or malignant cell organelles, ordisease causing organisms within a patient's body. Note that as usedherein and in the claims that follow, unless otherwise evident from thecontext, the term “abnormal tissue” is intended to encompass malignantcell organelles and disease causing organisms. Also attached to thesurface of microparticle core 12 are a plurality of photosensitizers 18of the type suitable for use in administering PDT.

[0026] Microparticle core 12 is coated with a polymer 16. Polymer 16increases the in vivo residence time of the antibody/photosensitizerconjugates within the patient's body, e.g., within the plasma, allowinga lower dose of the photosensitizer conjugate to be used, whilesimultaneously increasing the uptake of the antibody/photosensitizerconjugate by the abnormal tissue. Polymer 16 is preferably polyethyleneglycol (PEG) or PEG based, having a moderately high molecular weight,e.g., on the order of 20,000. Other polymers that exhibit similarproperties may also be used to extend the residence time of thephotosensitizer targeted conjugate within the patient's body. Thepolymer selected for this purpose must be: water soluble, hydrophilic,biocompatible, must exhibit a low toxicity, and must have a lowimmunogenicity. In addition, the polymer must not be biodegradable orform any toxic metabolites, must have a sufficiently high molecularweight, coupled with a highly flexible main chain, to provide forrelatively long in vivo residence times in a human body, e.g., for morethan several hours, and must be chemically compatible with thephotosensitizer and antibody used for the conjugate.

[0027] An understanding of how the polymer coating results in longer invivo residence times is helpful in designing a microparticle basedpolymer protected antibody/photosensitizer conjugate in accord with thepresent invention. Polymer 16 comprises a long, highly flexible mainchain and has a moderately high molecular weight (which means that themain chain is longer in length than most molecules). The flexible mainchain is in constant motion, creating a “cloud,” which protects thesurface of the microparticle and dramatically increases in vivoresidence times. However, this same “cloud” may also tend to inhibitantibody link sites 20 from successfully binding with correspondingantigens on the target abnormal tissue. The prior art teaches thatrelatively minor amounts (1-2 mol %) of a polymer such as PEG providesufficient protection to increase in vivo residence time, while higherconcentrations tend to inhibit antibody linking. It is thereforeanticipated that the optimal concentration of polymer used in producinga conjugate will need to be empirically determined for each differentmicroparticle based polymer protected antibody/photosensitizer conjugatespecies.

[0028]FIG. 2 illustrates how targeted polymer protectedantibody/photosensitizer conjugate 10 a is used for destroying amalignant cell organelle 22. In this Figure, targeted polymer protectedantibody/photosensitizer conjugate 10 a is shown with one of theantibody link sites 20 linked to an antigen 24 that is associated withthe malignant cell organelle. Because normal cells do not have anyantigen to which antibody link sites 20 will bind, targeted polymerprotected antibody/photosensitizer conjugates 10 a do not become boundto normal cells. After providing sufficient time for the targetedpolymer protected antibody/photosensitizer conjugates to bind to themalignant cell organelles or other types of abnormal tissue within apatient's body, a light 154 having a waveband corresponding to acharacteristic light absorption waveband of the photosensitizer isapplied using one of the techniques disclosed hereinbelow. This lightactivates a photosensitizer 18, causing it to form new chemical species,such as free oxygen radicals, which attack the target malignant cells orother abnormal tissue.

[0029]FIGS. 3A and 3B illustrate forms of polymer protectedantibody/photosensitizer conjugates, which do not incorporate amicroparticle core. In these embodiments, the antibody/photosensitizerconjugate is covalently bonded to the polymer rather than being attachedto a microparticle. FIG. 3A illustrates polymer protectedantibody/photosensitizer conjugate 10 b in which photosensitizer 18 iscovalently bonded to one attachment site of polymer 26 a, while theantibody which includes antibody link site 20 is covalently bonded to adifferent attachment site of polymer 26 a. Polymer 26 a is preferablyPEG, which has one attachment site at each end of the polymer chain.

[0030]FIG. 3B illustrates polymer protected antibody/photosensitizerconjugate 10 c in which photosensitizer 18 is covalently bonded to oneattachment site of polymer 26 b, while the antibody which includesantibody link site 20 is covalently bonded to photosensitizer 18.Polymer 26 b is preferably methyl-PEG, a PEG derivative which has only asingle attachment site at one end of the polymer chain; the otherattachment site having been replaced with a methyl group.

[0031] For the two forms of the polymer protectedantibody/photosensitizer conjugate respectively illustrated in FIGS. 3Aand 3B, it is important that antibody link site 20 be positioned in sucha manner as to allow it easy access to corresponding antigen 24 on thetargeted malignant cell organelle or other abnormal tissue, asillustrated in FIGS. 2 and 4. The relative positions of polymers 26 aand 26 b, antibody link site 20, and photosensitizer 18, as shown inFIGS. 3A and 3B, are not the only possible configurations. Actualpositional configurations of the conjugates will be a function of thepolymer chosen and the attachment sites available. Some polymers have aplurality of attachments sites available, thus a plurality of antibodylink sites 20 and/or photosensitizers 18 may be covalently bonded to asingle polymer molecule. The selection of polymer 26 a or 26 b will bebased on the chemical compatibility of the polymer, antibody 20, andphotosensitizer 18. Those skilled in the art will readily understandthat appropriate chemical manipulations and processes will be requiredto form the desired polymer protected antibody/photosensitizerconjugate, and the ease or difficulty of such manipulations andprocesses will factor decisively in the ultimate configuration of thepolymer protected antibody/photosensitizer conjugate employed.

[0032]FIG. 4 illustrates how targeted polymer protectedantibody/photosensitizer conjugate 10 c is used for destroying amalignant cell organelle 22. In a manner similar that of FIG. 2,targeted polymer protected antibody/photosensitizer conjugate 10 c isshown with antibody link site 20 bound to an antigen 24. After providingsufficient time for targeted conjugates 10 c to bind to the targetedabnormal tissue, light 154 of an appropriate waveband, i.e.,corresponding to the absorption waveband of the photosensitizer, isapplied using one of the techniques disclosed hereinbelow. The lightactivates photosensitizer 18, destroying the abnormal tissue.

Injection of Targeted Polymer Protected Antibody/PhotosensitizerConjugates

[0033] It is generally preferable to introduce the polymer protectedantibody/photosensitizer conjugates as close as possible to a treatmentsite, such as by introducing the polymer protectedantibody/photosensitizer conjugate directly into a tumor. At times, thelocation of a tumor or other treatment site is such that it is notfeasible to localize the administration of the polymer protectedantibody/photosensitizer conjugate. Furthermore, the targeted abnormaltissue may not be localized, but instead, may be viruses, microorganismsor metastasized cancer cells, which are more broadly distributedthroughout a patient's body. It is therefore contemplated that polymerprotected antibody/photosensitizer conjugates 10 a, 10 b, and 10 c maybe injected into the patient's bloodstream to allow the patient's owncirculatory system to deliver the polymer protectedantibody/photosensitizer conjugates to the targeted abnormal tissue. Asillustrated in FIG. 5, a syringe 58 can be used to inject a fluidcontaining the targeted polymer protected antibody/photosensitizerconjugates in suspension through a dermal layer 70 and into abloodstream 72. A needle 60 passes through dermal layer 70 and through awall 76 of bloodstream 72; fluid containing the targeted polymerprotected antibody/photosensitizer conjugates is injected through needle60 into blood 74. The blood flow in the vessel carries the targetedpolymer protected antibody/photosensitizer conjugates downstream, to oneor more locations where the targeted abnormal tissue is disposed. It isimportant to note that antibody link sites 20 will seek out and bindonly to the selected targeted abnormal tissue, which incorporatesantigen 24, as shown in FIGS. 2 and 4. Since the photosensitizer is notlinked to normal tissue, injury to normal tissue is minimized duringadministration of the light, particularly, if the light is administeredfrom an external source and must pass through normal tissue to reach theabnormal tissue that has been targeted.

Activation of the Photosensitizer

[0034] The photosensitizer in the polymer protectedantibody/photosensitizer conjugate destroys abnormal tissue to which itis bound when light of the proper waveband is administered. While themechanism by which PDT destroys cells is not fully understood, it isbelieved to produce free oxygen radicals that are toxic to the abnormaltissue.

[0035] In FIG. 6, a tumor 140 has been infused with polymer protectedantibody/photosensitizer conjugates 64. These conjugates may be of theforms illustrated in FIGS. 1, 3A, or 3B (i.e., conjugates 10 a, 10 b,and 10 c, respectively). The polymer protected antibody/photosensitizerconjugates can be infused either within a biocompatible fluid, such as aphysiological saline solution, or can be applied topically to theexterior surface of tumor 140. Tumor 140 lies within the patient's body,adjacent a dermal layer 144. Outside the patient's body, a power supply150 is coupled through a lead 148 to an external light array 146. Array146 comprises a plurality of light sources 152 such as LEDs. Whenenergized by power supply 150, light sources 152 emit light 154 of thedesired wavelength that passes freely through the dermal layer and intotumor 140, activating photosensitizer 18 that is included within polymerprotected antibody/photosensitizer conjugates 64, so thatphotosensitizer 18 produces substances that attack tumor 140.

[0036]FIG. 7 illustrates yet another technique for exposing polymerprotected antibody/photosensitizer conjugates 64 to light 154 of thewaveband corresponding to the light absorption waveband of thephotosensitizer. In this approach, a probe 160 is insertedinterstitially within tumor 140. Probe 160 includes a linear array 162of LEDs (or other appropriate light sources) that are energized througha lead 164. Lead 164 is coupled to a remote internal (or external) powersupply (not shown). If disposed internally, the power supply can beenergized using an external power source that is electromagneticallycoupled to the internal power supply. A detailed description ofapparatus suitable for providing such electromagnetic coupling isprovided in U.S. Pat. No. 5,715,837, which is assigned to the sameassignee as the present invention, the disclosure and drawings of whichare hereby specifically incorporated herein by reference.

[0037] As noted above, the targeted abnormal tissue may not be alocalized tumor, but instead, may comprise metastasized cancer cells,disease causing viruses, disease causing bacteria or other undesirablemicroorganisms that are distributed throughout at least a portion of thepatient's body. In this instance, the light employed for administeringthe light therapy preferably has a relatively long wavelength, e.g.,longer than 800 nm, to enable the light to pass through several cm. oftissue. Generally, the longer the wavelength of the light, the greaterits ability to penetrate tissue in the body of the patient. Of course,the light adsorption waveband of the photosensitizer must be matched tothe wavelength or waveband of the light that is administered to activatethe photosensitizer. It is contemplated that by passing a longwavelength light source over the external surfaces of a patient's body,the majority of the polymer protected antibody/photosensitizerconjugates attached to targeted abnormal tissue may be activated, thusdestroying the abnormal tissue, even though widely disseminated withinthe patient's body.

[0038] It is also contemplated that polymer protectedantibody/photosensitizer conjugates can be employed prophylactically toprevent the development of abnormal tissue at a prospective treatmentsite. For example, it is now possible to identify women withsusceptibility to certain types of breast cancer based upon genetictesting. The probabilities of developing breast cancer in a women whohas tested positive for the susceptible genes is so significant thatsome women choose to undergo prophylactic radical mastectomy to minimizethe risk of later developing breast cancer. Instead, the presentinvention can provide an alternative prophylaxis, by providing forrepetitive administration of a polymer protectedantibody/photosensitizer conjugate targeted at the type of canceroustumor cells that might develop, followed by administration of lighttherapy using light having a waveband corresponding to the lightadsorption waveband of the photosensitizer. By periodically repeatingsuch prophylactic therapy, development of cancerous tumor cells in thewoman's breast can likely be prevented, but without the trauma involvedin undergoing a radical mastectomy.

[0039] Another application of the present invention is for destroyingany residual abnormal tissue that may remain at a tumor resection site,following surgical removal of the tumor. A common problem following suchsurgery is the regrowth of the tumor. After administering a polymerprotected antibody/photosensitizer conjugate targeted at antibodies ofthe tumor that was removed, light therapy can be administered to destroythe residual tumor cells that have linked with the conjugate, therebypreventing the regrowth of the tumor. Such post-surgical treatment mightbe rendered, for example, following a mastectomy or brain tumor removal.

[0040] Yet another application of the present invention is in thetreatment of leukemia or other diseases requiring bone marrowtransplant. A polymer protected antibody/photosensitizer conjugatetargeted at malignant antigens in the bone marrow can be administeredfollowed by administration of light therapy using light of theappropriate waveband, as noted above. This treatment should be effectiveboth pre- and post-bone marrow transplant to destroy much of theabnormal tissue causing the leukemia, and may be employed, in additionto more conventional radiation and chemotherapy treatments. It is alsocontemplated that the present invention may be used for destroyingabnormal tissue in bone marrow, thereby avoiding the need for a bonemarrow transplant. The polymer protected antibody/photosensitizerconjugate may be activated with light administered either from aninterstitial source or an external source, i.e., transcutaneously orfrom within the patient's body.

[0041] While empirical evidence such as may be developed by clinicaltrials of the present invention have not yet been provided, it isbelieved by some authorities that antibodies like those used in thepolymer protected antibody/photosensitizer conjugate may activate thebody's own immune system. Furthermore, photodynamic activation of aphotosensitizer has been demonstrated to also cause an immune response.It is expected that the present invention will produce a synergisticeffect in enhancing the efficacy of PDT that is far greater than eitherof these processes alone. The use of a polymer such as PEG to protect atargeted photosensitizer is also expected to provide a much greaterimprovement in the efficacy of the conjugate than might be expectedrelative to the use of a PEG photosensitizer conjugate alone or atargeted photosensitizer alone.

[0042] Although the present invention has been described in connectionwith the preferred forms of practicing it and modifications thereto,those of ordinary skill in the art will understand that many othermodifications can be made within the scope of the claims that follow.Accordingly, it is not intended that the scope of the invention in anyway be limited by the above description, but instead be determinedentirely by reference to the claims that follow.

The invention in which an exclusive right is claimed is defined by thefollowing:
 1. A method for destroying abnormal tissue in a patient, atan internal treatment site, comprising the steps of: (a) providing apolymer protected antibody/photosensitizer conjugate, thephotosensitizer portion characterized by absorbing light within adefined waveband, the polymer portion characterized by having a highmolecular weight combined with a highly flexible main chain, therebyproviding steric protection to the conjugate, and the antibody portioncharacterized by being targeted to an antigen which exists substantiallyonly at the abnormal tissue in the patient; (b) administering thepolymer protected antibody/photosensitizer conjugate to the patient,said antibody linking with the abnormal tissue at the treatment site,and said polymer increasing an in vivo residence time of theantibody/photosensitizer conjugate to allow for an increased uptake ofthe antibody/photosensitizer conjugate by the abnormal tissue at thetreatment site; and (c) administering light within the defined wavebandto the internal treatment site, said light activating thephotosensitizer to destroy the abnormal tissue.
 2. The method of claim 1, wherein the polymer comprises polyethylene glycol.
 3. The method ofclaim 1 , wherein the polymer comprises a derivative of polyethyleneglycol.
 4. The method of claim 1 , wherein the polymer is water solubleand hydrophilic.
 5. The method of claim 1 , wherein the polymer isbiocompatible, exhibiting a low toxicity and a low immunogenicity in aconcentration administered to the patient.
 6. The method of claim 1 ,wherein the polymer must have at least one attachment site to which thephotosensitizer and the antibody covalently bond.
 7. The method of claim1 , wherein the defined waveband includes wavelengths sufficiently longto readily pass through a dermal layer of the patient.
 8. The method ofclaim 7 , wherein the light is administered externally to a body of thepatient and passes through intervening tissue to reach the internaltreatment site.
 9. The method of claim 8 , wherein the abnormal tissueis distributed throughout at least a portion of a body of the patient.10. The method of claim 8 , wherein the treatment site includes at leastpart of a vascular system of the patient, said abnormal tissue beingdisposed within said at least part of the vascular system.
 11. Themethod of claim 1 , wherein the abnormal tissue includes at least one ofa disease causing bacteria and a disease causing virus.
 12. The methodof claim 1 , wherein the step of administering the light includes thestep of inserting a light source that emits light interstitially withinthe internal treatment site so that the light is administered to theinternal treatment site.
 13. The method of claim 1 , wherein theinternal treatment site is a prospective treatment site at whichabnormal tissue may possibly develop, further comprising the steps of:(a) administering the polymer protected antibody/photosensitizerconjugate to the patient; and (b) as a prophylaxis, administering thelight to the prospective treatment site.
 14. The method of claim 13 ,wherein the steps of administering the polymer protectedantibody/photosensitizer conjugate and administering the light as aprophylaxis are repeated at spaced-apart intervals of time to preventdevelopment of the abnormal tissue at the prospective treatment sitefrom occurring.
 15. The method of claim 1 , further comprising the stepof surgically excising a substantial portion of the abnormal tissue,followed by the steps of administering the polymer protectedantibody/photosensitizer conjugate, and administering the light, todestroy any residual abnormal tissue at the treatment site.
 16. Themethod of claim 1 , further comprising the step of transplanting bonemarrow into the patient, followed by the steps of administering thepolymer protected antibody/photosensitizer conjugate, and administeringthe light, to destroy residual abnormal tissue in the patient.
 17. Amethod for improving a specificity and an extent with which aphotosensitizer is taken up by abnormal tissue within a patient,compared to normal tissue, comprising the steps of: (a) providing amicroparticle, a photosensitizer, an antibody that is targeted atantigens of the abnormal tissue, and a polymer; (b) conjugating saidantibody and said photosensitizer to said microparticle, forming amicroparticle based antibody/photosensitizer conjugate that is adaptedto link with the abnormal tissue; (c) coating said microparticle basedantibody/photosensitizer conjugate with a polymer forming a polymercoated microparticle based antibody/photosensitizer conjugate that ischaracterized by a prolonged in vivo residence time for themicroparticle based antibody/photosensitizer conjugate in the patient;and (d) administering the polymer coated microparticle basedantibody/photosensitizer conjugate to the patient, so that said antibodyon the microparticle based antibody/photosensitizer conjugate links withthe abnormal tissue, uptake of the polymer coated microparticle basedantibody/photosensitizer conjugate by the abnormal tissue beingsubstantially improved compared with a microparticle basedantibody/photosensitizer conjugate that is not coated by the polymer anduptake of the polymer coated microparticle basedantibody/photosensitizer conjugate by the normal tissue beingsubstantially reduced compared with a microparticle basedphotosensitizer that is coated by the polymer.
 18. The method of claim17 , wherein the microparticle comprises one of a micelle and asubstantially inert carrier core.
 19. The method of claim 17 , whereinthe polymer is polyethylene glycol.
 20. A method for improving aspecificity with which a photosensitizer is taken up by abnormal tissuewithin a patient, comprising the steps of: (a) providing aphotosensitizer, an antibody that is targeted at antigens present at thetargeted treatment site, and a polymer that is water soluble,hydrophilic, of sufficiently high molecular weight, characterized byhaving a highly flexible main chain, which provides for an extended invivo residence time in a human body, and capable of forming at least onecovalent bond with the photosensitizer and antibody; (b) conjugating theantibody and photosensitizer with the polymer to form apolymer/antibody/photosensitizer conjugate; and (c) administering thepolymer/antibody/photosensitizer conjugate to the patient, so that theantibody on the polymer/antibody/photosensitizer conjugate links withthe abnormal tissue during the extended in vivo residence time,substantially improving uptake of the polymer/antibody/photosensitizerconjugate by the abnormal tissue.
 21. The method of claim 20 , whereinthe polymer is polyethylene glycol.
 22. A method for enhancing anefficacy of a light therapy rendered to destroy abnormal tissue,comprising the steps of: (a) administering polyethylene glycol (PEG) anda photosensitizer that is conjugated with an antibody targeted to bindwith antigens present on the abnormal tissue, said polyethylene glycolserving to extend a viable lifetime of a resultingPEG/photosensitizer/antibody conjugate to enable more of said antibodyto bind with the antigens on the abnormal tissue, thereby increasing anuptake of the PEG/photosensitizer/antibody conjugate by the abnormaltissue; and (b) after sufficient time has elapsed followingadministration of the PEG/photosensitizer/antibody conjugate to permitthe antibody to bind with the antigens, administering a light therapy,said light therapy activating the photosensitizer and more effectivelydestroying the abnormal tissue due to the increased uptake of thePEG/photosensitizer/antibody conjugate by the abnormal tissue.
 23. Themethod of claim 22 , wherein the PEG/photosensitizer/antibody conjugatecomprises a microparticle of conjugated photosensitizer and antibodycoated with said PEG.
 24. The method of claim 22 , wherein conjugatedphotosensitizer and antibody is covalently bonded to said PEG.
 25. Themethod of claim 22 , wherein conjugated photosensitizer and antibody arecovalently bonded to different sites on said PEG.